U.S. patent application number 09/846769 was filed with the patent office on 2003-02-13 for method and system for terminating atrial fibrillation by inducing a ventricular extra-systole with combipolar pacing.
Invention is credited to Kupper, Bernhard C.H..
Application Number | 20030032986 09/846769 |
Document ID | / |
Family ID | 25298895 |
Filed Date | 2003-02-13 |
United States Patent
Application |
20030032986 |
Kind Code |
A1 |
Kupper, Bernhard C.H. |
February 13, 2003 |
Method and system for terminating atrial fibrillation by inducing a
ventricular extra-systole with combipolar pacing
Abstract
A method and system for pacing cardiac tissue is provided.
Atrial fibrillation is detected in the cardiac tissue. An area of
the cardiac tissue is paced with at least one atrial electrode and
simultaneously paced with at least one ventricular electrode. A
ventricular extra-systole is induced, thereby terminating the
atrial fibrillation.
Inventors: |
Kupper, Bernhard C.H.;
(Dusseldorf, DE) |
Correspondence
Address: |
MEDTRONIC, INC.
710 MEDTRONIC PARKWAY NE
MS-LC340
MINNEAPOLIS
MN
55432-5604
US
|
Family ID: |
25298895 |
Appl. No.: |
09/846769 |
Filed: |
April 30, 2001 |
Current U.S.
Class: |
607/5 |
Current CPC
Class: |
A61N 1/39622 20170801;
A61N 1/395 20130101 |
Class at
Publication: |
607/5 |
International
Class: |
A61N 001/39 |
Claims
We claim:
1. A method of pacing cardiac tissue using an implantable medical
device, comprising: detecting atrial fibrillation in the cardiac
tissue; pacing an area of the cardiac tissue with at least one
atrial electrode; simultaneously pacing the area of the cardiac
tissue with at least one ventricular electrode; and inducing a
ventricular extra-systole.
2. The method of claim 1, further comprising: terminating the
atrial fibrillation by inducing the ventricular extra-systole.
3. The method of claim 1 further comprising: sensing the
ventricular extra-systole.
4. The method of claim 1 further comprising: simultaneously pacing
the area of the cardiac tissue for a duration.
5. The method of claim 4 further comprising: determining the
duration.
6. The method of claim 1 further comprising: pacing the cardiac
tissue at a regular function.
7. The method of claim 4 further comprising: pacing the cardiac
tissue at a regular function once the duration is over.
8. The method of claim 1 further comprising: adjusting a rate at
which the area of the cardiac tissue is paced with the at least one
atrial electrode.
9. The method of claim 8 further comprising: adjusting a rate at
which the area of the cardiac tissue is paced with the at least one
ventricular electrode.
10. The method of claim 1 further comprising: adjusting a rate at
which the area of the cardiac tissue is paced with the at least one
ventricular electrode.
11. The method of claim 1 further comprising: stopping pacing of
the area of cardiac tissue with the at least one atrial electrode
once the ventricular extra-systole has been sensed.
12. The method of claim 1 further comprising: stopping pacing of
the area of cardiac tissue with the at least one ventricular
electrode once the ventricular extra-systole has been sensed.
13. An implantable medical device, comprising: a processor; at
least one pacing circuit operably connected to the processor; at
least one atrial electrode operably connected to the processor and
adapted for placement within an atrium of a heart; and at least one
ventricular electrode operably connected to the processor and
adapted for placement within a ventricle of the heart wherein an
area of the heart is simultaneous paced with the atrial electrode
and the ventricular electrode to induce a ventricular
extra-systole.
14. The device of claim 13 wherein the atrial electrode is
operatively adapted to sense an atrial fibrillation.
15. The device of claim 13 wherein the ventricular electrode is
operatively adapted to sense an atrial fibrillation.
16. The device of claim 13 further comprising: at least one sensing
electrode.
17. The device of claim 13 further comprising: a memory operably
connected to the processor.
18. An implantable medical system, comprising: means for detecting
atrial fibrillation in the cardiac tissue; means for pacing an area
of the cardiac tissue with at least one atrial electrode; means for
simultaneously pacing the area of the cardiac tissue with at least
one ventricular electrode; and means for inducing a ventricular
extra-systole.
19. The system of claim 18, further comprising: means for
terminating the atrial fibrillation by inducing the ventricular
extra-systole.
20. The system of claim 18 further comprising: means for sensing
the ventricular extra-systole.
21. The system of claim 18 further comprising: means for
simultaneously pacing the area of the cardiac tissue for a
duration.
22. The system of claim 21 further comprising: means for
determining the duration.
23. The system of claim 18 further comprising: means for pacing the
cardiac tissue at a regular function.
24. The system of claim 21 further comprising: means for pacing the
cardiac tissue at a regular function once the duration is over.
25. The system of claim 18 further comprising: means for adjusting
a rate at which the area of the cardiac tissue is paced with the at
least one atrial electrode.
26. The system of claim 25 further comprising: means for adjusting
a rate at which the area of the cardiac tissue is paced with the at
least one ventricular electrode.
27. The system of claim 18 further comprising: means for adjusting
a rate at which the area of the cardiac tissue is paced with the at
least one ventricular electrode.
28. The system of claim 18 further comprising: means for stopping
pacing of the area of cardiac tissue with the at least one atrial
electrode once the ventricular extra-systole has been sensed.
29. The system of claim 18 further comprising: means for stopping
pacing of the area of cardiac tissue with the at least one
ventricular electrode once the ventricular extra-systole has been
sensed.
30. A computer usable medium including a program for pacing cardiac
tissue, comprising: computer program code that detects atrial
fibrillation in the cardiac tissue; computer program code that
paces an area of the cardiac tissue with at least one atrial
electrode; computer program code that simultaneously paces the area
of the cardiac tissue with at least one ventricular electrode; and
computer program code that induces a ventricular extra-systole.
31. The program of claim 30, further comprising: computer program
code that terminates the atrial fibrillation by inducing the
ventricular extra-systole.
32. The program of claim 30 further comprising: computer program
code that senses the ventricular extra-systole.
33. The program of claim 30 further comprising: computer program
code that simultaneously paces the area of the cardiac tissue for a
duration.
34. The program of claim 33 further comprising: computer program
code that determines the duration.
35. The program of claim 30 further comprising: computer program
code that paces the cardiac tissue at a regular function.
36. The program of claim 35 further comprising: computer program
code that paces the cardiac tissue at a regular function once the
duration is over.
37. The program of claim 30 further comprising: computer program
code that adjusts a rate at which the area of the cardiac tissue is
paced with the at least one atrial electrode.
38. The program of claim 37 further comprising: computer program
code that adjusts a rate at which the area of the cardiac tissue is
paced with the at least one ventricular electrode.
39. The program of claim 30 further comprising: computer program
code that adjusts a rate at which the area of the cardiac tissue is
paced with the at least one ventricular electrode.
40. The program of claim 30 further comprising: computer program
code that stops pacing of the area of cardiac tissue with the at
least one atrial electrode once the ventricular extra-systole has
been sensed.
41. The program of claim 30 further comprising: computer program
code that stops pacing of the area of cardiac tissue with the at
least one ventricular electrode once the ventricular extra-systole
has been sensed.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to the field of implantable
medical devices. More particularly, the present invention relates
to cardiac pacing systems that provide a method for using pacing
pulses to terminate an atrial fibrillation by inducing a
ventricular extra-systole through combipolar pacing.
BACKGROUND OF THE INVENTION
[0002] Tachyarrhythmias are episodes of high-rate cardiac
depolarizations. Tachyarrhythmias may occur in one chamber of the
heart or may be propagated from one chamber to another. Some
tachyarrhythmias are sufficiently high in rate to compromise
cardiac output from the chamber(s) affected, leading to loss
consciousness or death, in the case of ventricular fibrillation or
weakness and dizziness in the case of atrial fibrillation. Atrial
fibrillation is often debilitating, due to the loss of atrial
cardiac output, and may sometimes lead to ventricular
fibrillation.
[0003] Generally, fibrillation may be terminated by administering
high energy level cardioversion/defibrillation shocks or pulses
until the fibrillation is terminated. For example, in the context
of implantable anti-arrhythmia devices, these pulses may be applied
by means of large surface area electrodes on or in the chamber to
be defibrillated. However, the high energy level pulses are often
sufficient to cause pain to the patient. Thus, it would be
desirable to prevent or decrease the occurrence of atrial
fibrillation.
[0004] Thus, some exploration has been made in the use of pacing
level pulses, which stimulate the cardiac tissue at much lower
levels than defibrillation pulses, to terminate atrial
fibrillation. Implantable pulse generators (IPGs) that deliver
pacing level pulses are well known in the art. These IPGs may
deliver pulses to one or more chambers of the heart. However, in
many cases, the low level pacing pulses are not sufficient to
terminate atrial fibrillation.
[0005] Some exploration has also been made into the possibilities
of using ventricular extra-systoles (also known as premature
ventricular contractions or PVCs) to capture the atrium and
terminate atrial fibrillation.
[0006] Some IPGs are dual-chamber, having both atrial and
ventricular leads, while other IPGs are multiple-chamber, having
one or more leads in two or more chambers of the heart. Such
dual-chamber or multiple chamber IPGs have one or more unipolar or
bipolar leads in the ventricle and one or more unipolar or bipolar
leads in the atrium of the right and/or the left side of the heart.
Sensing of cardiac activity takes place either between a tip and a
ring of one or more electrodes in a given chamber or between the
tip of one or more electrodes in a given chamber and the can of the
IPG. Another type of sensing, sometimes called as "combipolar"
sensing, takes place between the respective tip electrodes of these
unipolar or bipolar leads.
[0007] The pacing pulses delivered from such dual-chamber leads and
multiple-chamber IPGs may be too low in energy to serve as
defibrillation pulses.
[0008] However, these IPGs may also pace atrial cardiac tissue with
the atrial lead and may pace ventricular tissue with the
ventricular lead. The leads of a dual-chamber or a multiple-chamber
IPG may also pace tissue between the leads and thereby deliver
energy to the ventricle to induce a ventricular extra-systole
(VES), also called a premature ventricular contraction (PVC). This
type of pacing may simultaneously delivery enough energy to the
atria to induce atrial depolarization in the same instance as the
VES is being induced.
[0009] The close coupling of the premature ventricular action
induced by the combipolar pulse to the start of an atrial
arrhythmia may induce arise in atrial pressure. This rise further
results in a higher wall tension in the atria thus causing an
electrical situation whereas the delivery of energy is more likely
to capture the highest possible number of atrial cells.
Additionally, the pacing pulses that result from such combipolar
pacing may have a higher amplitude and/or pulse width than the
usual pacing pulses.
[0010] Thus, a need exists in the medical arts for use of
combipolar pacing of cardiac tissue to induce a ventricular
extra-systole in order to simultaneously terminate atrial
fibrillation of the cardiac tissue.
[0011] Some methods have been proposed in the prior art for
administering pacing pulses to cardiac tissue in order to terminate
atrial fibrillation.
[0012] For example, U.S. Pat. Nos. 5,562,708 and 5,674,251, both to
Combs et al., disclose a pacemaker system adapted to deliver pacing
pulses in the presence of fibrillation. An extended pulse train is
delivered in order to gradually entrain greater portions of heart
tissue, until a sufficient percentage of tissue is entrained to
interrupt fibrillation.
[0013] U.S. Pat. No. 5,683,429 to Mehra discloses a method and
apparatus for preventing fibrillation by distributing sense
electrodes one or both atrial chambers. The sense electrodes may be
used to sense an atrial premature beat and then to distribute a
pacing energy pulse burst simultaneously.
[0014] The article "Les stimulateurs cardiaques destins traiter les
tachycardies paroxystiques" (Cardiac stimulators for treating
paroxysmal tachycardias)" in the journal Stimucoeur Medical by J.
F. Leclercq et al. discloses the use of a pacemaker stimulating an
atria and a ventricle simultaneously to terminate an arrhythmia in
the case of drug-resistant paroxysmal reciprocating
tachycardia.
[0015] Some methods have also been proposed in the prior art for
combipolar sensing. For example, U.S. Pat. No. 5,871,507 to Obel,
et al. discloses the use of signal morphology analysis to detect
signals between unipolar atrial and ventricular leads.
[0016] The most pertinent prior art patents and publications known
at the present time are shown in the following table:
1TABLE 1 Prior Art Publications Pat. No. Date Inventor(s) 5,562,708
Oct. 8, 1996 Combs et al. 5,674,251 Oct. 7, 1997 Combs et al.
5,683,429 Nov. 4, 1997 Mehra 5,871,507 Feb. 16, 1999 Obel et
al.
[0017] J. F. Leclercq, et al. (1979) "Les stimulateurs cardiaques
destins traiter les tachycardies paroxystiques" (Cardiac
stimulators for treating paroxysmal tachycardias)", Stimucoeur
Medical, Volume 7, No.1, pp. 8-15
[0018] The publications listed in Table 1 are hereby incorporated
by reference herein, each in its entirety. As those of ordinary
skill in the art will appreciate readily upon reading the Summary
of the Invention, the Detailed Description of the Preferred
Embodiments and the Claims set forth below, at least some of the
devices and methods disclosed in the patent of Table 1 may be
modified advantageously in accordance with the teachings of the
present invention.
SUMMARY OF THE INVENTION
[0019] The present invention is therefore directed to providing a
method and system for terminating atrial fibrillation by inducing a
ventricular extra-systole through combipolar pacing. The system of
the present invention overcomes at least some of the problems,
disadvantages and limitations of the prior art described above, and
provides a more efficient and accurate means of terminating atrial
fibrillation by inducing a ventricular extra-systole.
[0020] The present invention has certain objects. That is, various
embodiments of the present invention provide solutions to one or
more problems existing in the prior art respecting the pacing of
cardiac tissue. Those problems include, without limitation: (a)
patients experiencing discomfort while treatment for atrial
fibrillation is being administered; (b) atrial fibrillation being
terminated using energy pulses which are uncomfortably high or
excessive; (c) pacing energy pulses being less effective in the
termination of atrial fibrillation than desired; (d) difficulty in
administering high energy stimulus pulses to treat atrial
fibrillation, and (e) difficulty in providing pacing pulses of
sufficient amplitude and pulse width to cause atrial
depolarization.
[0021] In comparison to known pacing techniques, various
embodiments of the present invention provide one or more of the
following advantages: (a) the use of pacing energy level pulses,
rather than high energy pulse shocks, to treat atrial fibrillation;
(b) the ability to create pacing pulses of higher amplitude or
pulse width, and (c) fewer patient complaints of discomfort in the
treatment of fibrillation.
[0022] Some embodiments of the present invention include one or
more of the following features: (a) an IPG capable of treating
atrial fibrillation by inducing ventricular extra-systole; (b) an
IPG capable of delivering pacing energy level pulses of a higher
amplitude or pulse width; (c) methods of treating atrial
fibrillation with pacing energy level pulses rather than high
energy shocks and (d) methods of inducing ventricular extra-systole
sufficient to terminate atrial fibrillation without causing
distress to the patient.
[0023] At least some embodiments of the present invention involve
detecting atrial fibrillation in the cardiac tissue. Immediately
following detection of atrial fibrillation, an area of the
ventricle is simultaneously paced at least one pacing pulse is
delivered to an area of the ventricle simultaneously from at least
one atrial electrode and at least one ventricular electrode. This
simultaneous combipolar pacing induces a ventricular extra-systole
for the duration in order to terminate the atrial fibrillation.
After the duration ends, the occurrence of atrial fibrillation is
again measured. If atrial fibrillation is still detected, another
combipolar pacing pulse is administered.
[0024] The ventricular extra-systole may be sensed. The
simultaneous pacing may occur for a duration, which may be
determined using any suitable means. The cardiac tissue may also be
paced at a regular function, particular once the duration is over.
The rates of pacing with the at least one atrial electrode and/or
the at least one ventricular electrode may be adjusted.
Simultaneous, combipolar pacing of the area of cardiac tissue may
be stopped once the ventricular extra-systole has been delivered
and redetection of the atrial rhythm shows an regular function.
BRIEF DESCRIPTION OF THE DRAWINGS
[0025] The above, and other objects, advantages and features of the
present invention will be more readily understood from the
following detailed description of the preferred embodiments when
considered in conjunction with the drawings, in which like
reference numerals indicate identical structures throughout the
several views, and wherein:
[0026] FIG. 1 is a schematic view of one embodiment of an
implantable medical device in situ, made in accordance with the
present invention;
[0027] FIG. 2 is another schematic view of an embodiment of the
implantable medical device of FIG. 1, made in accordance with the
present invention;
[0028] FIG. 3 is a block diagram illustrating components of an
embodiment of the implantable medical device of FIG. 1, made in
accordance with the present invention;
[0029] FIG. 4 is a schematic view of another embodiment of an
implantable medical device, made in accordance with the present
invention;
[0030] FIG. 5 is a block diagram illustrating components of an
embodiment of the implantable medical device of FIG. 4, made in
accordance with the present invention;
[0031] FIG. 6 is a flow diagram of one embodiment of a method for
terminating atrial fibrillation in accordance with the present
invention; and
[0032] FIG. 7 is a flow diagram of another embodiment of a method
for terminating atrial fibrillation in accordance with the present
invention.
DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS
[0033] It is to be understood that the terms "IPG" and "IMD", as
employed in the specification and claims hereof, means an
implantable medical device capable of delivering electrical stimuli
to cardiac tissue, and includes within its scope pacemakers, PCDs,
ICDs, etc.
[0034] FIG. 1 is a simplified schematic view of one embodiment of
implantable medical device ("IMD") 10 of the present invention. IMD
10 shown in FIG. 1 is a pacemaker comprising at least one of pacing
and sensing leads 16 and 18 attached to hermetically sealed
enclosure 14 and implanted near human or mammalian heart 8. Pacing
and sensing leads 16 and 18 sense electrical signals attendant to
the depolarization and re-polarization of the heart 8, and further
provide pacing pulses for causing depolarization of cardiac tissue
in the vicinity of the distal ends thereof. Leads 16 and 18 may
have unipolar or bipolar electrodes disposed thereon, as is well
known in the art. In one embodiment of the invention, leads 16 and
18 are adapted to administer combipolar pacing pulses to cardiac
tissue. For example, lead 16 may be adapted to administer pacing
pulses as an atrial lead and lead 18 may be adapted to administer
pacing pulses as a ventricular lead, or vice versa. Examples of IMD
10 include implantable cardiac pacemakers disclosed in U.S. Pat.
No. 5,158,078 to Bennett et al., U.S. Pat. No. 5,312,453 to Shelton
et al. or U.S. Pat. No. 5,144,949 to Olson, all of which are hereby
incorporated by reference herein, each in its respective
entirety.
[0035] FIG. 2 shows connector module 12 and hermetically sealed
enclosure 14 of IMD 10 located in and near human or mammalian heart
8. Atrial and ventricular pacing leads 16 and 18 extend from
connector header module 12 to the right atrium and ventricle,
respectively, of heart 8. Atrial electrodes 20 and 21 disposed at
the distal end of atrial pacing lead 16 are located in the right
atrium. Ventricular electrodes 28 and 29 at the distal end of
ventricular pacing lead 18 are located in the right ventricle.
[0036] FIG. 3 shows a block diagram illustrating the constituent
components of IMD 10 in accordance with one embodiment of the
present invention, where IMD 10 is a pacemaker having a
microprocessor-based architecture. IMD 10 is shown as including
activity sensor or accelerometer 11, which may be an accelerometer
bonded to a hybrid circuit located inside enclosure 14. Activity
sensor 11 typically (although not necessarily) provides a sensor
output that varies as a function of a measured parameter relating
to a patient's metabolic requirements. For the sake of convenience,
IMD 10 in FIG. 3 is shown with lead 18 only connected thereto;
similar circuitry and connections not explicitly shown in FIG. 3
apply to lead 16.
[0037] IMD 10 in FIG. 3 may be programmable by means of an external
programming unit (not shown in the Figures). One such programmer is
the commercially available Medtronic Model 9790 programmer, which
is microprocessor-based and provides a series of encoded signals to
IMD 10, typically through a programming head which transmits or
telemeters radio-frequency (RF) encoded signals to IMD 10. Such a
telemetry system is described in U.S. Pat. No. 5,312,453 to Wyborny
et al., hereby incorporated by reference herein in its entirety.
The programming methodology disclosed in U.S. Pat. No. 5,312,453 to
Wyborny et al. is identified herein for illustrative purposes only.
Any of a number of suitable programming and telemetry methodologies
known in the art may be employed so long as the desired information
is transmitted to and from the pacemaker.
[0038] As shown in FIG. 3, lead 18 is coupled to node 50 in IMD 10
through input capacitor 52. Activity sensor or accelerometer 11 may
be attached to a hybrid circuit located inside hermetically sealed
enclosure 14 of IMD 10. The output signal provided by activity
sensor 11 is coupled to input/output circuit 54. Input/output
circuit 54 contains analog circuits for interfacing to heart 8,
activity sensor 11, antenna 56 and circuits for the application of
stimulating pulses to heart 8. Accordingly, the rate at which heart
8 is stimulated or beats spontaneously without stimulation may be
controlled and/or monitored using software-implemented algorithms
or pacing rate functions stored in microcomputer circuit 58. In one
embodiment of the invention, the stimulating pulses are applied in
a combipolar pacing fashion, in which pacing occurs between the
atrial and ventricular leads.
[0039] Microcomputer circuit 58 may comprise on-board circuit 60
and off-board circuit 62. Circuit 58 may correspond to a
microcomputer circuit disclosed in U.S. Pat. No. 5,312,453 to
Shelton et al., hereby incorporated by reference herein in its
entirety. On-board circuit 60 may include microprocessor 64, system
clock circuit 66 and on-board RAM 68 and ROM 70. Off-board circuit
62 may comprise a RAM/ROM unit. On-board circuit 60 and off-board
circuit 62 are each coupled by data communication bus 72 to digital
controller/timer circuit 74. Microcomputer circuit 58 may comprise
a custom integrated circuit device augmented by standard RAM/ROM
components.
[0040] Electrical components shown in FIG. 3 are powered by an
appropriate implantable battery power source 76 in accordance with
common practice in the art. For the sake of clarity, the coupling
of battery power to the various components of IMD 10 is not shown
in the Figures. Antenna 56 is connected to input/output circuit 54
to permit uplink/downlink telemetry through RF transmitter and
receiver telemetry unit 78. By way of example, telemetry unit 78
may correspond to that disclosed in U.S. Pat. No. 4,566,063, issued
to Thompson et al., hereby incorporated by reference herein in its
entirety, or to that disclosed in the above-referenced '453 patent
to Wyborny et al. It is generally preferred that the particular
programming and telemetry scheme selected permit the entry and
storage of cardiac rate-response parameters. The specific
embodiments of antenna 56, input/output circuit 54 and telemetry
unit 78 presented herein are shown for illustrative purposes only,
and are not intended to limit the scope of the present
invention.
[0041] Continuing to refer to FIG. 3, V.sub.REF and Bias circuit 82
may generate stable voltage reference and bias currents for analog
circuits included in input/output circuit 54. Analog-to-digital
converter (ADC) and multiplexer unit 84 digitizes analog signals
and voltages to provide "real-time" telemetry intracardiac signals
and battery end-of-life (EOL) replacement functions. Operating
commands for controlling the timing of IMD 10 are coupled by data
communication bus 72 to digital controller/timer circuit 74, where
digital timers and counters establish the overall escape interval
of the IMD 10 as well as various refractory, blanking and other
timing windows for controlling the operation of peripheral
components disposed within input/output circuit 54.
[0042] Digital controller/timer circuit 74 may be coupled to
sensing circuitry, including sense amplifier 88, peak sense and
threshold measurement unit 90 and comparator/threshold detector 92.
Circuit 74 may further be coupled to electrogram (EGM) amplifier 94
for receiving amplified and processed signals sensed by lead 18.
Sense amplifier 88 amplifies sensed electrical cardiac signals and
provides an amplified signal to peak sense and threshold
measurement circuitry 90, which in turn provides an indication of
peak sensed voltages and measured sense amplifier threshold
voltages on multiple conductor signal path 67 to digital
controller/timer circuit 74. An amplified sense amplifier signal is
then provided to comparator/threshold detector 92. By way of
example, sense amplifier 88 may correspond to that disclosed in
U.S. Pat. No. 4,379,459 to Stein, hereby incorporated by reference
herein in its entirety.
[0043] The electrogram signal provided by EGM amplifier 94 is
employed when IMD 10 is being interrogated by an external
programmer to transmit a representation of a cardiac analog
electrogram. See, for example, U.S. Pat. No. 4,556,063 to Thompson
et al., hereby incorporated by reference herein in its entirety.
Output pulse generator 96 provides pacing stimuli to patient's
heart 8 through coupling capacitor 98 in response to a pacing
trigger signal provided by digital controller/timer circuit 74 each
time the escape interval times out, an externally transmitted
pacing command is received or in response to other stored commands
as is well known in the pacing art. By way of example, output
amplifier 96 may correspond generally to an output amplifier
disclosed in U.S. Pat. No. 4,476,868 to Thompson, hereby
incorporated by reference herein in its entirety.
[0044] The specific embodiments of input amplifier 88, output
amplifier 96 and EGM amplifier 94 identified herein are presented
for illustrative purposes only, and are not intended to be limiting
in respect of the scope of the present invention. The specific
embodiments of such circuits may not be critical to practicing some
embodiments of the present invention so long as they provide means
for generating a stimulating pulse and are capable of providing
signals indicative of natural or stimulated contractions of heart
8.
[0045] In some preferred embodiments of the present invention, IMD
10 may operate in various non-rate-responsive modes, including, but
not limited to, DDD, DDI, VVI, VOO and UVT modes. In other
preferred embodiments of the present invention, IMD 10 may operate
in various rate-responsive, including, but not limited to, DDDR,
DDIR, VVIR, VOOR and VVTR modes. Some embodiments of the present
invention are capable of operating in both non-rate-responsive and
rate responsive modes. Moreover, in various embodiments of the
present invention IMD 10 may be programmably configured to operate
so that it varies the rate at which it delivers stimulating pulses
to heart 8 only in response to one or more selected sensor outputs
being generated. In one embodiment of the invention, IMD 10 is
capable of operating in response to the sensing of atrial
fibrillation in order to terminate the fibrillation. Numerous
pacemaker features and functions not explicitly mentioned herein
may be incorporated into IMD 10 while remaining within the scope of
the present invention.
[0046] The present invention is not limited in scope to
single-sensor or dual-sensor pacemakers, and is not limited to IMDs
comprising activity or pressure sensors only. Nor is the present
invention limited in scope to single-chamber pacemakers,
single-chamber leads for pacemakers or single-sensor or dual-sensor
leads for pacemakers. Thus, various embodiments of the present
invention may be practiced in conjunction with more than two leads
or with multiple-chamber pacemakers, for example. At least some
embodiments of the present invention may be applied equally well in
the contexts of single-, dual-, triple- or quadruple-chamber
pacemakers or other types of IMDs. One embodiment of the invention
is applied in the context of a dual-chamber pacemaker with at least
one atrial least and at least one ventricular lead. See, for
example, U.S. Pat. No. 5,800,465 to Thompson et al., hereby
incorporated by reference herein in its entirety, as are all U.S.
Patents referenced therein.
[0047] IMD 10 may also be a pacemaker-cardioverter-defibrillator
("PCD") corresponding to any of numerous commercially available
implantable PCDs. Various embodiments of the present invention may
be practiced in conjunction with PCDs such as those disclosed in
U.S. Pat. No. 5,545,186 to Olson et al., U.S. Pat. No. 5,354,316 to
Keimel, U.S. Pat. No. 5,314,430 to Bardy, U.S. Pat. No. 5,131,388
to Pless and U.S. Pat. No. 4,821,723 to Baker et al., all of which
are hereby incorporated by reference herein, each in its respective
entirety.
[0048] FIGS. 4 and 5 illustrate one embodiment of IMD 10 and a
corresponding lead set of the present invention, where IMD 10 is a
PCD. In FIG. 4, the ventricular lead takes the form of leads
disclosed in U.S. Pat. Nos. 5,099,838 and 5,314,430 to Bardy, and
includes an elongated insulative lead body 1 carrying three
concentric coiled conductors separated from one another by tubular
insulative sheaths. Located adjacent the distal end of lead 1 are
ring electrode 2, extendable helix electrode 3 mounted retractably
within insulative electrode head 4 and elongated coil electrode 5.
Each of the electrodes is coupled to one of the coiled conductors
within lead body 1. Electrodes 2 and 3 may be employed for cardiac
pacing and for sensing ventricular depolarizations. Electrodes 2
and 3 may also be employed for administering combipolar pacing
pulses in order to induce a ventricular extra-systole.
[0049] At the proximal end of the lead is bifurcated connector 6,
which carries three electrical connectors, each coupled to one of
the coiled conductors. Defibrillation electrode 5 may be fabricated
from platinum, platinum alloy or other materials known to be usable
in implantable defibrillation electrodes and may be about 5 cm in
length. In one embodiment of the invention, defibrillation
electrodes 5 may be used to aid in the administration of
stimulating pulses to induce a ventricular extra-systole.
[0050] The atrial/SVC lead shown in FIG. 4 includes elongated
insulative lead body 7 carrying three concentric coiled conductors
separated from one another by tubular insulative sheaths
corresponding to the structure of the ventricular lead. Located
adjacent the J-shaped distal end of the lead are ring electrode 9
and extendable helix electrode 13 mounted retractably within an
insulative electrode head 15. Each of the electrodes is coupled to
one of the coiled conductors within lead body 7. Electrodes 13 and
9 may be employed for atrial pacing and for sensing atrial
depolarizations. Electrodes 9 and 13 may also be employed for
administering combipolar pacing pulses in order to induce a
ventricular extra-systole. Elongated coil electrode 19 is provided
proximal to electrode 9 and coupled to the third conductor within
lead body 7. In one embodiment of the invention, electrode 19 is 10
cm in length or greater and is configured to extend from the SVC
toward the tricuspid valve. In one embodiment of the present
invention, approximately 5 cm of the right atrium/SVC electrode is
located in the right atrium with the remaining 5 cm located in the
SVC. At the proximal end of the lead is bifurcated connector 17,
which carries three electrical connectors, each coupled to one of
the coiled conductors.
[0051] The coronary sinus lead shown in FIG. 4 assumes the form of
a coronary sinus lead disclosed in the above cited '838 patent
issued to Bardy, and includes elongated insulative lead body 41
carrying one coiled conductor coupled to an elongated coiled
defibrillation electrode 21. Electrode 21, illustrated in broken
outline in FIG. 4, is located within the coronary sinus and the
great vein of the heart. At the proximal end of the lead is
connector plug 23 carrying an electrical connector coupled to the
coiled conductor. The coronary sinus/great vein electrode 41 may be
about 5 cm in length.
[0052] Implantable PCD 10 is shown in FIG. 4 in combination with
leads 1, 7 and 41, and lead connector assemblies 23, 17 and 6
inserted into connector block 12. Optionally, insulation of the
outward facing portion of housing 14 of PCD 10 may be provided
using a plastic coating such as parylene or silicone rubber, as is
employed in some unipolar cardiac pacemakers. The outward facing
portion, however, may be left uninsulated or some other division
between insulated and uninsulated portions may be employed. The
uninsulated portion of housing 14 serves as a subcutaneous
defibrillation electrode to defibrillate either the atria or
ventricles. Lead configurations other than those shown in FIG. 4
may be practiced in conjunction with the present invention, such as
those shown in U.S. Pat. No. 5,690,686 to Min et al., hereby
incorporated by reference herein in its entirety.
[0053] FIG. 5 is a functional schematic diagram of one embodiment
of implantable PCD 10 of the present invention. This diagram should
be taken as exemplary of the type of device in which various
embodiments of the present invention may be embodied, and not as
limiting, as it is believed that the invention may be practiced in
a wide variety of device implementations, including cardioverter
and defibrillators which do not provide anti-tachycardia pacing
therapies.
[0054] IMD 10 is provided with an electrode system. If the
electrode configuration of FIG. 4 is employed, the correspondence
to the illustrated electrodes is as follows. Electrode 25 in FIG. 5
includes the uninsulated portion of the housing of PCD 10.
Electrodes 25, 15, 21 and 5 are coupled to high voltage output
circuit 27, which includes high voltage switches controlled by
CV/defib control logic 29 via control bus 31. Switches disposed
within circuit 27 determine which electrodes are employed and which
electrodes are coupled to the positive and negative terminals of
the capacitor bank (which includes capacitors 33 and 35) during
delivery of defibrillation pulses.
[0055] Electrodes 2 and 3 are located on or in the ventricle and
are coupled to the R-wave amplifier 37, which may take the form of
an automatic gain controlled amplifier providing an adjustable
sensing threshold as a function of the measured R-wave amplitude. A
signal is generated on R-out line 39 whenever the signal sensed
between electrodes 2 and 3 exceeds the present sensing threshold.
In one embodiment of the invention, at least one of electrodes 2, 3
is used in a combipolar pacing fashion to induce a ventricular
extra-systole in conjunction with one of the atrial electrodes
described below.
[0056] Electrodes 9 and 13 are located on or in the atrium and are
coupled to the P-wave amplifier 43, which may also take the form of
an automatic gain controlled amplifier providing an adjustable
sensing threshold as a function of the measured P-wave amplitude. A
signal is generated on P-out line 45 whenever the signal sensed
between electrodes 9 and 13 exceeds the present sensing threshold.
The general operation of R-wave and P-wave amplifiers 37 and 43 may
correspond to that disclosed in U.S. Pat. No. 5,117,824, by Keimel
et al., issued Jun. 2, 1992, for "An Apparatus for Monitoring
Electrical Physiologic Signals", hereby incorporated by reference
herein in its entirety. In one embodiment of the invention, at
least one of electrodes 9 or 13 is used in a combipolar pacing
fashion to induce a ventricular extra-systole in conjunction with
one of the ventricular electrodes described above.
[0057] Switch matrix 47 is used to select which of the available
electrodes are coupled to wide band (0.5-200 Hz) amplifier 49 for
use in digital signal analysis. Selection of electrodes is
controlled by the microprocessor 51 via data/address bus 53, which
selections may be varied as desired. Signals from the electrodes
selected for coupling to bandpass amplifier 49 are provided to
multiplexer 55, and thereafter converted to multi-bit digital
signals by A/D converter 57, for storage in random access memory 59
under control of direct memory access circuit 61. Microprocessor 51
may employ digital signal analysis techniques to characterize the
digitized signals stored in random access memory 59 to recognize
and classify the patient's heart rhythm employing any of the
numerous signal-processing methodologies known to the art.
[0058] The remainder of the circuitry is dedicated to the provision
of cardiac pacing, cardioversion and defibrillation therapies, and,
for purposes of the present invention, may correspond to circuitry
known to those skilled in the art. The following exemplary
apparatus is disclosed for accomplishing pacing, cardioversion and
defibrillation functions. Pacer timing/control circuitry 63 may
include programmable digital counters which control the basic time
intervals associated with DDD, VVI, DVI, VDD, AAI, DDI and other
modes of single and dual chamber pacing well known to the art.
Circuitry 63 also may control escape intervals associated with
anti-tachyarrhythmia pacing in both the atrium and the ventricle,
employing any anti-tachyarrhythmia pacing therapies known to the
art. Circuitry 63 may also be used to administer combipolar pacing
in accordance with the present invention.
[0059] Intervals defined by pacing circuitry 63 include atrial and
ventricular pacing escape intervals, the refractory periods during
which sensed P-waves and R-waves are ineffective to restart timing
of the escape intervals and the pulse widths of the pacing pulses
and combipolar pacing escape intervals. The durations of these
intervals are determined by microprocessor 51, in response to
stored data in memory 59 and are communicated to pacing circuitry
63 via address/data bus 53. Pacer circuitry 63 also determines the
amplitude of the cardiac pacing pulses under control of
microprocessor 51. Pacer circuitry 63 may also determine the
amplitude of the combipolar pacing pulses administered under
control of microprocessor 51.
[0060] During pacing, escape interval counters within pacer
timing/control circuitry 63 are reset upon sensing of R-waves and
P-waves as indicated by signals on lines 39 and 45, and in
accordance with the selected mode of pacing on time-out trigger
generation of pacing pulses by pacer output circuitry 65 and 67,
which are coupled to electrodes 9, 13, 2 and 3. Escape interval
counters are also reset on generation of pacing pulses and thereby
control the basic timing of cardiac pacing functions, including
anti-tachyarrhythmia pacing. The durations of the intervals defined
by escape interval timers are determined by microprocessor 51 via
data/address bus 53. The value of the count present in the escape
interval counters when reset by sensed R-waves and P-waves may be
used to measure the durations of R-R intervals, P-P intervals, P-R
intervals and R-P intervals, which measurements are stored in
memory 59 and used to detect the presence of tachyarrhythmias.
[0061] Microprocessor 51 may operate as an interrupt driven device,
and may be responsive to interrupts from pacer timing/control
circuitry 63 corresponding to the occurrence of sensed P-waves and
R-waves and corresponding to the generation of cardiac pacing
pulses. Those interrupts are provided via data/address bus 53. Any
necessary mathematical calculations to be performed by
microprocessor 51 and any updating of the values or intervals
controlled by pacer timing/control circuitry 63 take place
following such interrupts.
[0062] Detection of atrial or ventricular tachyarrhythmias, as
employed in the present invention, may correspond to any of the
various tachyarrhythmia detection algorithms presently known in the
art. For example, the presence of an atrial or ventricular
tachyarrhythmia may be confirmed by detecting a sustained series of
short R-R or P-P intervals of an average rate indicative of
tachyarrhythmia or an unbroken series of short R-R or P-P
intervals. The suddenness of onset of the detected high rates, the
stability of the high rates, and a number of other factors known in
the art may also be measured at this time. Appropriate ventricular
tachyarrhythmia detection methodologies measuring such factors are
described in U.S. Pat. No. 4,726,380 issued to Vollmann, U.S. Pat.
No. 4,880,005, issued to Pless et al. and U.S. Pat. No. 4,830,006,
issued to Haluska et al., all hereby incorporated by reference
herein, each in its respective entirety. An additional set of
tachycardia recognition methodologies is disclosed in the article
"Onset and Stability for Ventricular Tachyarrhythmia Detection in
an Implantable Pacer-Cardioverter-Defibrillator" by Olson et al.,
published in Computers in Cardiology, Oct. 7-10, 1986, IEEE
Computer Society Press, pages 167-170, also incorporated by
reference herein in its entirety. Atrial fibrillation detection
methodologies are disclosed in Published PCT Application Ser. No.
US92/02829, Publication No. WO92/18198, by Adams et al., and in the
article "Automatic Tachycardia Recognition", by Arzbaecher et al.,
published in PACE, May-June, 1984, pp. 541-547, both of which are
hereby incorporated by reference herein, each in its respective
entirety.
[0063] In the event an atrial or ventricular tachyarrhythmia is
detected and an anti-tachyarrhythmia pacing regimen is desired,
appropriate timing intervals for controlling generation of
anti-tachyarrhythmia pacing therapies are loaded from
microprocessor 51 into the pacer timing and control circuitry 63,
to control the operation of the escape interval counters therein
and to define refractory periods during which detection of R-waves
and P-waves is ineffective to restart the escape interval
counters.
[0064] Alternatively, circuitry for controlling the timing and
generation of anti-tachycardia pacing pulses as described in U.S.
Pat. No. 4,577,633, issued to Berkovits et al. on Mar. 25, 1986,
U.S. Pat. No. 4,880,005, issued to Pless et al. on Nov. 14, 1989,
U.S. Pat. No. 4,726,380, issued to Vollmann et al. on Feb. 23, 1988
and U.S. Pat. No. 4,587,970, issued to Holley et al. on May 13,
1986, all of which are hereby incorporated herein by reference,
each in its respective entirety, may also be employed.
[0065] In the event that generation of a cardioversion or
defibrillation pulse is required, microprocessor 51 may employ an
escape interval counter to control timing of such cardioversion and
defibrillation pulses, as well as associated refractory periods. In
response to the detection of atrial or ventricular fibrillation or
tachyarrhythmia requiring a cardioversion pulse, microprocessor 51
activates cardioversion/defibrillation control circuitry 29, which
initiates charging of the high voltage capacitors 33 and 35 via
charging circuit 69, under the control of high voltage charging
control line 71. The voltage on the high voltage capacitors is
monitored via VCAP line 73, which is passed through multiplexer 55
and in response to reaching a predetermined value set by
microprocessor 51, results in generation of a logic signal on Cap
Full (CF) line 77 to terminate charging. Thereafter, timing of the
delivery of the defibrillation or cardioversion pulse is controlled
by pacer timing/control circuitry 63. Following delivery of the
fibrillation or tachycardia therapy, microprocessor 51 returns the
device to a cardiac pacing mode and awaits the next successive
interrupt due to pacing or the occurrence of a sensed atrial or
ventricular depolarization.
[0066] Alternatively, microprocessor 51 may employ an escape
interval counter to control timing of combipolar pacing pulses
between an atrial and a ventricular lead, such as leads 16 and 18,
respectively, as well as associated refractory periods. In response
to the detection of atrial or ventricular fibrillation or
tachyarrhythmia requiring stimulation to terminate fibrillation,
microprocessor 51 activates combipolar pacing control circuitry
(which may be part of circuitry 63). The atrial lead and the
ventricular lead then pace the tissue between them. This creates a
field, which induces a ventricular extra-systole. Thereafter,
timing of the delivery of the combipolar pacing pulse is controlled
by pacer timing/control circuitry 63. For example, several
combipolar pacing pulses may be delivered before a ventricular
extra-systole and termination of atrial fibrillation is achieved.
Alternatively, the amplitude of the combipolar pacing pulse may be
modified in order to achieve the desired ventricular extra-systole.
Alternatively, the pulse width of the combipolar pacing pulse may
be modified in order to achieve the desired ventricular
extra-systole.
[0067] Following delivery of the fibrillation or tachycardia
therapy, microprocessor 51 returns the device to a cardiac pacing
mode and awaits the next successive interrupt due to pacing or the
occurrence of a sensed atrial or ventricular depolarization.
[0068] Several embodiments of appropriate systems for the delivery
and synchronization of ventricular cardioversion and defibrillation
pulses and for controlling the timing functions related to them are
disclosed in U.S. Pat. No. 5,188,105 to Keimel, U.S. Pat. No.
5,269,298 to Adams et al. and U.S. Pat. No. 4,316,472 to Mirowski
et al., all of which are hereby incorporated by reference herein,
each in its respective entirety. Any known cardioversion or
defibrillation pulse control circuitry is believed to be usable in
conjunction with various embodiments of the present invention,
however. For example, circuitry controlling the timing and
generation of cardioversion and defibrillation pulses such as that
disclosed in U.S. Pat. No. 4,384,585 to Zipes, U.S. Pat. No.
4,949,719 to Pless et al., or U.S. Pat. No. 4,375,817 to Engle et
al., all of which are hereby incorporated by reference herein, each
in its respective entirety, may also be employed.
[0069] Continuing to refer to FIG. 5, delivery of cardioversion or
defibrillation pulses may be accomplished by output circuit 27
under the control of control circuitry 29 via control bus 31.
Output circuit 27 determines whether a monophasic or biphasic pulse
is delivered, the polarity of the electrodes and which electrodes
are involved in delivery of the pulse. Output circuit 27 also
includes high voltage switches, which control whether electrodes
are coupled together during delivery of the pulse. Alternatively,
electrodes intended to be coupled together during the pulse may
simply be permanently coupled to one another, either exterior to or
within the interior of the device housing, and polarity may
similarly be pre-set, as in current implantable defibrillators. An
example of output circuitry for delivery of biphasic pulse regimens
to multiple electrode systems may be found in U.S. Pat. No.
4,953,551, issued to Mehra, and in U.S. Pat. No. 4,727,877, both of
which are hereby incorporated by reference herein in its
entirety.
[0070] An example of circuitry that may be used to control delivery
of monophasic pulses is disclosed in U.S. Pat. No. 5,163,427 to
Keimel, also hereby incorporated by reference herein in its
entirety. Output control circuitry similar to that disclosed in
U.S. Pat. No. 4,953,551 to Mehra et al. or U.S. Pat. No. 4,800,883
to Winstrom, both incorporated by reference, each in its respective
entirety, may also be used in conjunction with various embodiments
of the present invention to deliver biphasic pulses.
[0071] Alternatively, IMD 10 may be an implantable nerve stimulator
or muscle stimulator such as that disclosed in U.S. Pat. No.
5,199,428 to Obel et al., U.S. Pat. No. 5,207,218 to Carpentier et
al. or U.S. Pat. No. 5,330,507 to Schwartz, or an implantable
monitoring device such as that disclosed in U.S. Pat. No. 5,331,966
issued to Bennet et al., all of which are hereby incorporated by
reference herein, each in its respective entirety. The present
invention is believed to find wide application to any form of
implantable electrical device for use in conjunction with
electrical leads.
[0072] FIG. 6 illustrates one embodiment of a method for
terminating atrial fibrillation in accordance with the present
invention. As discussed above, the method of the present invention
may be performed under the control of any appropriate computer
algorithm stored in a memory or a portion of a memory of
microcomputer 58 in IMD 10. Such a computer algorithm may be any
program capable of being stored in an electronic medium such as, by
way of example only, RAM 68 or ROM 70 of IMD 10, where the contents
of RAM 68 and ROM 70 may be accessed and consequently executed by
microprocessor 64/microcomputer 58.
[0073] At block 610, the cardiac tissue is paced at a regular
pacing function. In one embodiment of the invention, the regular
pacing function comprises pacing in a non-combipolar pacing
fashion. Regular pacing function may be determined and set by a
physician, may be based on the patient's medical history, may be a
preprogrammed pacing function, may be selected from a look-up table
or database, or calculated based on data gathered by IMD 10. Thus,
at block 610, the right atrium may be paced by an electrode located
within the right atrium, for example, atrial electrode 9, 13.
Alternatively, the left atrium may be paced by an electrode located
within the left atrium, for example, atrial electrode 9, 13.
Meanwhile, the right ventricle may be paced by an electrode located
within the right ventricle, for example, ventricular electrode 2,
3. Alternatively, the left ventricle may be paced by an electrode
located within the left ventricle, for example, ventricular
electrode 2, 3.
[0074] At block 615, it may be determined whether atrial
fibrillation is detected. This may be determined using any suitable
method known in the arts. For example, the sensing of a premature
atrial contraction (PAC) or a premature ventricular contraction
(PVC) is known in the art to indicate that atrial fibrillation is
occurring. The PAC/PVC may be sensed, for example, by one or more
of the sensing leads described above or by activity sensor 11. The
occurrence of atrial fibrillation may be determined, for example,
by an appropriate computer algorithm stored in memory or a portion
of memory of microcomputer 58 of IMD 10. If no atrial fibrillation
is detected, the method returns to block 610 and the heart is paced
at its regular pacing function. Alternatively, the heart may be
paced at any suitable value if no atrial fibrillation occurs.
[0075] In one embodiment of the invention, an atrial arrhythmia
that may indicate the onset of atrial fibrillation may be detected
at block 615. For example, the first beat to start an atrial
arrhythmia may succeed the last series of sinus beats by at least
270-280 ms. Thus, the first beat of an atrial arrhythmia will have
the defined shortest interval for a given patient. This may be, for
example, a PAC. So, in one embodiment of the invention, a given
patient may have a minimum interval preprogrammed or predetermined
for IMD 10. This shortest interval may be determined and set by a
physician, may be based on the patient's medical history, may be a
preprogrammed pacing interval, may be selected from a look-up table
or database, or calculated based on data gathered by IMD 10. If an
interval detected by IMD 10 is less than this shortest interval,
atrial fibrillation may have occurred and the method will proceed
to block 620. Generally, the drop to this shortest interval is
sudden and the interval is markedly shorter than the previous
interval. Graph A below illustrates one example, based on clinical
data, of such a sudden rate drop, which may be indicative of the
onset of atrial fibrillation.
[0076] In an alternate embodiment of the invention, a plurality of
atrial arrhythmias that may indicate the onset of atrial
fibrillation may be detected at block 615. A first beat of an
atrial arrhythmia may be detected, for example, because its
interval is less than the shortest interval defined for the patient
as described above. Then, IMD 10 may evaluate whether at least one
more beat of atrial arrhythmia occurs succeeding the first beat
detected above. If IMD 10 detects more than one atrial arrhythmia,
i.e., a series of atrial arrhythmias, then atrial fibrillation may
have occurred and the method will proceed to block 620. In one
embodiment of the invention, two detected atrial arrhythmia beats
will cause the method to proceed to block 620. Alternatively, three
detected atrial arrhythmia beats will cause the method to proceed
to block 620. Alternatively, any suitable number of detected beats
may be used. For example, Graph B below illustrates one example,
based on clinical data, of such multiple preceding PACs which may
be indicative of the onset of atrial fibrillation. In Graph B, four
preceding detected atrial arrhythmia beats (four PACs) are
shown.
[0077] In other embodiments of the invention, IMD 10 may determine
the length of the interval between the first detected atrial
arrhythmia beat and the beat following the first detected atrial
arrhythmia beat and/or the length of the interval between any two
subsequent detected beats. The length of this interval may also be
compared to the shortest interval determined for the patient. If
the determined interval is shorter than the shortest interval and
is then followed by a longer interval (sometimes called a post-PAC
interval) atrial fibrillation may have occurred and the method will
proceed to block 620. In one embodiment of the invention, two
detected atrial arrhythmia beats short intervals may be followed by
a longer interval and will also cause the method to proceed to
block 620. Alternatively, any combination of detected atrial
arrhythmia beats with an interval shorter than the shortest
interval determined for the patient followed by a long post-PAC
interval will cause the method to proceed to block 620.
Alternatively, any interval determined between two of any suitable
number of detected beats may be used. For example, Graph C below
illustrates one example, based on clinical data, of such short-long
interval combinations, which may be indicative of the onset of
atrial fibrillation.
[0078] Thus, atrial arrhythmia may be detected within two to three
actions of the first detected atrial arrhythmia beat.
[0079] If atrial fibrillation is detected, the method may proceed
to block 620, when a first combipolar pacing therapy is delivered
to the ventricle. This may take the form of, for example, a single
combipolar pacing pulse. Combipolar pacing may be accomplished
using any suitable method known in the arts. In one embodiment,
leads 16 and 18 described above may be adapted to administer
combipolar pacing pulses to cardiac tissue. For example, lead 16
may be adapted to administer pacing pulses as an atrial lead and
lead 18 may be adapted to administer pacing pulses as a ventricular
lead, or vice versa. Thus, lead 16 and lead 18 may administer a
combipolar pulse by pacing at least one of the ventricles
simultaneously. In at least some embodiments of the invention, a
combipolar pulse may also be delivered in an alternating fashion,
for example, the ventricle may be paced with lead 16 and
immediately after with lead 18 or with lead 18 followed by lead 16.
In some embodiments of the invention, combipolar pacing is
preferably administered to the right ventricle. Alternatively a
combipolar pacing pulse may be administered to an area of the right
ventricle which bypasses right ventricle outflow tracks.
Alternatively, a combipolar pacing pulse may be administered to the
apex of the right ventricular sinus.
[0080] Alternatively, at least one of ventricular electrodes 2, 3
is used in a combipolar pacing fashion to induce a ventricular
extra-systole in conjunction with at least one of the atrial
electrodes 9, 13. Thus ventricular electrode 2,3 and atrial
electrode 9, 13 may administer a combipolar pulse by pacing at
least one of the ventricles simultaneously. In at least some
embodiments of the invention, a combipolar pulse may also be
delivered in an alternating fashion, for example, the ventricle may
be paced with ventricular electrode 2,3 and then with atrial
electrodes 9, 13 or vice versa, i.e., with atrial electrodes 9, 13
followed by ventricular electrodes 2, 3. In some embodiments of the
invention, combipolar pacing is preferably administered to the
right ventricle. Alternatively a combipolar pacing pulse may be
administered to an area of the right ventricle which bypasses right
ventricle outflow tracks. Alternatively, a combipolar pacing pulse
may be administered to the apex of the right ventricular sinus.
[0081] In another embodiment of the invention ring electrode 2 may
be adapted to administer pacing pulses as an atrial lead and coil
electrode 5 may be adapted to administer pacing pulses as a
ventricular lead, or vice versa. Thus, electrode 2 and electrode 5
may administer a combipolar pulse by pacing at least one of the
ventricles simultaneously. In at least some embodiments of the
invention, a combipolar pulse may also be delivered in an
alternating fashion, for example, the ventricle may be paced with
electrode 2 followed by electrode 5 or vice versa, i.e., the
ventricle may be paced with electrode 5 followed by electrode 2. In
some embodiments of the invention, combipolar pacing is preferably
administered to the right ventricle. Alternatively a combipolar
pacing pulse may be administered to an area of the right ventricle
which bypasses right ventricle outflow tracks. Alternatively, a
combipolar pacing pulse may be administered to the apex of the
right ventricular sinus.
[0082] In one embodiment of the invention, circuitry 63 may be used
to administer a combipolar pacing pulse by controlling pulses
delivered from one or more electrodes.
[0083] The combipolar pacing therapy preferably delivers an
effective amount of energy sufficient to terminate atrial
fibrillation. The combipolar pacing may create a field in the area
between the atrial and the ventricular leads. This field may cause
the paces delivered by one or more of the atrial and/or ventricular
leads to have a higher than normal amplitude or pulse width.
Alternatively, a low energy pulse may be delivered from the
combination of atrial and ventricular electrodes. In one embodiment
of the invention, each of the electrodes delivers the maximum
energy it is capable of delivering during administration of its
first combipolar pacing pulse. Alternatively, a combination of low
and high energy pulses may be administered as a first combipolar
pacing pulse. In one embodiment of the invention, the first
combipolar pacing pulse is administered for a duration long enough
to cause a ventricular extra-systole. In at least some embodiments
of the invention, a ventricular action is initiated after a 600 ms
duration. Other possible ranges of duration include, but are not
limited to 200 to 1000 ms, 300 to 900 ms, 400 to 800 ms, 500 to 700
ms and 550 to 650 ms.
[0084] At block 625, it may be determined if a ventricular
extra-systole has been induced. The ventricular extra-systole may
be sensed with any of the sensing electrodes described above. In
one embodiment of the invention, the ventricular extra-systole is
induced by the combipolar pacing of block 620. Detection of a
ventricular extra-systole may be accomplished using any suitable
method known in the arts. In one embodiment, one or more of sensing
leads 16 and 18 and/or activity sensor 11 described above may be
adapted to sense a ventricular extra-systole. Alternatively, at
least one of ventricular electrodes 2, 3 may sense the ventricular
extra-systole. In one embodiment of the invention, circuitry 63 may
be used to determine if a ventricular extra-systole has been
sensed.
[0085] In one embodiment of the invention, the ventricular
extra-systole will have a interval shorter than the ordinary
ventricular interval of the patient. This ordinary interval may be
determined and set by a physician, may be based on the patient's
medical history, may be a preprogrammed pacing interval, may be
selected from a look-up table or database, or calculated based on
data gathered by IMD 10.
[0086] In at least some embodiments of the invention, IMD 10 may
determine the given interval of the first two or more detected
atrial arrhythmia beats and will trigger delivery of the first
combipolar pacing therapy so that it is administered on at a point
in time which corresponds to the determined interval minus a
selectable percentage of the determined interval, i.e.,
2 time of combipolar = determined - percentage of pacing interval
interval determined interval
[0087] This percentage may be based on the vulnerable phase of the
T-wave. The T-wave phase may be sensed, for example using sensor 11
or the sensing electrodes described above. Alternatively, the
percentage may be calculated from a programmable dynamic refractory
period. This calculation may be accomplished, for example under the
control of any appropriate computer algorithm stored in a memory or
a portion of a memory of microcomputer 58 in IMD 10. Such a
computer algorithm may be any program capable of being stored in an
electronic medium such as, by way of example only, RAM 68 or ROM 70
of IMD 10, where the contents of RAM 68 and ROM 70 may be accessed
and consequently executed by microprocessor 64/microcomputer
58.
[0088] If a not induced ventricular action is detected with the
desired predetermined ordinary interval, a ventricular
extra-systole may have occurred and the method may proceed to block
635. If a ventricular action is detected with an interval shorter
than the predetermined ordinary interval concurrently succeeded by
one or more ventricular actions with intervals equal to or shorter
than the predetermined ordinary interval, a ventricular-couplet or
run may have occurred and the method may proceed to block 635.
[0089] At block 635, it may again be determined whether atrial
fibrillation is occurring. This may be determined using any
suitable method known in the arts. For example, the sensing of a
premature atrial contraction (PAC) or a premature ventricular
contraction (PVC) is known in the art to indicate that atrial
fibrillation is occurring. The PAC/PVC may be sensed, for example,
by one or more of the sensing leads described above or by activity
sensor 11. The occurrence of atrial fibrillation may be determined,
for example, by an appropriate computer algorithm stored in memory
or a portion of memory of microcomputer 58 of IMD 10. If atrial
fibrillation is no longer detected, the method returns to block 610
and the heart is paced at its regular pacing function.
Alternatively, the heart may be paced at any suitable value once
atrial fibrillation has been terminated. Before or while the heart
returns to ordinary pacing function, data regarding the number of
combipolar pacing therapies administered and the efficacy of the
therapies administered may be stored for later retrieval and
evaluation at block 650. This data may be stored, for example, in a
storage location of IMD 10, including but not limited to, a
location of memory 59 and/or RAM 68.
[0090] At block 635, determination if atrial fibrillation is still
occurring may be made using the methods described above and
illustrated in Graphs A-C, i.e., detecting an atrial arrhythmia
that may indicate the onset of atrial fibrillation, detecting an
atrial arrhythmia with an interval shorter than an predetermined
interval established for the patient, detecting a plurality of
atrial arrhythmias, and/or measuring the intervals of a plurality
of atrial arrhythmias. In another embodiment of the invention, IMD
10 may redetect the atrium and re-tune to the existing cycle
length. IMD 10 may then evaluate whether the existing cycle length
represents atrial arrhythmia.
[0091] If atrial fibrillation is still detected, the method may
proceed to block 640, when a next combipolar pacing therapy is
delivered to the ventricle. This make take the form of, for
example, a single combipolar pacing pulse. Combipolar pacing may be
accomplished using any suitable method known in the arts.
Combipolar pacing may be accomplished as described above using
leads 16 and 18, ventricular electrodes 2, 3 and atrial electrodes
9, 13, or using ring electrode 2 and coil electrode 5.
[0092] In one embodiment of the invention, circuitry 63 may be used
to administer a combipolar pacing pulse by controlling pulses
delivered from one or more electrodes.
[0093] The combipolar pacing therapy preferably delivers an
effective amount of energy sufficient to terminate atrial
fibrillation. The combipolar pacing may create a field in the area
between the atrial and the ventricular leads. In some embodiments
of the invention, the field is created by delivering high amplitude
energy and using a broad pulse width. Alternatively, a low energy
pulse may be delivered from the combination of atrial and
ventricular electrodes. In one embodiment of the invention, each of
the electrodes delivers the maximum energy it is capable of
delivering during administration of the next combipolar pacing
pulse. Alternatively, a combination of low and high energy pulses
may be administered as the next combipolar pacing pulse.
Alternatively, the amount of energy administered may be modified
based on the amount of energy delivered with the first combipolar
pacing therapy. For example, the next combipolar pacing pulse
delivered at block 640 may be of a lower or higher energy than the
first combipolar pacing therapy delivered at block 620.
[0094] In one embodiment of the invention, the next combipolar
pacing pulse is administered for a duration long enough to cause a
ventricular extra-systole. In at least some embodiments of the
invention, a ventricular action is initiated after a 600 ms
duration. Other possible ranges of duration include, but are not
limited to 200 to 1000 ms, 300 to 900 ms, 400 to 800 ms, 500 to 700
ms and 550 to 650 ms.
[0095] At block 645, the number of combipolar pacing therapies
delivered is calculated. Generally, only a limited number of
combipolar pacing therapies may be applied to cause ventricular
extra-systole. Moreover, administration of combipolar pacing
therapies may generally be successful in termination of atrial
fibrillation after the first, second or third delivery. Thus, at
block 645, it is determined if the number of combipolar pacing
therapies delivered exceeds a particular limit. For example, the
limit may be x number of combipolar pacing therapies. In one
embodiment of the invention, x may equal any suitable number for
ensuring optimal therapeutic benefit to the patient including, but
not limited to a maximum of 4 combipolar therapies, 3 combipolar
therapies and 2 combipolar therapies.
[0096] If the number of combipolar therapies delivered does not
exceed the limit set at block 645, the method may proceed to block
635 as indicated by the loop at 647. At block 635, it may again be
determined whether atrial fibrillation is occurring. This may be
determined using any suitable method known in the arts or described
above. If atrial fibrillation is no longer detected, the method
returns to block 610 and the heart is paced at its regular pacing
function. Alternatively, the heart may be paced at any suitable
value once atrial fibrillation has been terminated. Before or while
the heart returns to ordinary pacing function, data regarding the
number of combipolar pacing therapies administered and the efficacy
of the therapies administered may be stored for later retrieval and
evaluation at block 650. This data may be stored, for example, in a
storage location of IMD 10, including but not limited to, a
location of memory 59 and/or RAM 68.
[0097] If atrial fibrillation is still detected, the method may
proceed to block 640, when a next combipolar pacing therapy is
delivered to the ventricle. The loop indicated at 647 may be
repeated until administration of combipolar pacing therapy
effectively terminates atrial fibrillation or until the limit of
combipolar pacing therapies indicated at block 645 is exceeded.
[0098] At block 645, when the limit of combipolar pacing therapies
has been exceeded, the method may return to block 610 and the heart
is paced at its regular pacing function. Alternatively, the heart
may be paced at any suitable value once atrial fibrillation has
been terminated. Before or while the heart returns to ordinary
pacing function, data regarding the number of combipolar pacing
therapies administered and the efficacy of the therapies
administered may be stored for later retrieval and evaluation at
block 650. This data may be stored, for example, in a storage
location of IMD 10, including but not limited to, a location of
memory 59 and/or RAM 68.
[0099] FIG. 7 illustrates one embodiment of a method for
terminating atrial fibrillation in accordance with the present
invention. As discussed above, the method of the present invention
may be performed under the control of any appropriate computer
algorithm stored in a memory or a portion of a memory of
microcomputer 58 in IMD 10. Such a computer algorithm may be any
program capable of being stored in an electronic medium such as, by
way of example only, RAM 68 or ROM 70 of IMD 10, where the contents
of RAM 68 and ROM 70 may be accessed and consequently executed by
microprocessor 64/microcomputer 58.
[0100] At block 710, the cardiac tissue is paced at a regular
pacing function. In one embodiment of the invention, the regular
pacing function comprises pacing in a non-combipolar pacing
fashion. Regular pacing function may be determined and set by a
physician, may be based on the patient's medical history, may be a
preprogrammed pacing function, may be selected from a look-up table
or database, or calculated based on data gathered by IMD 10. Thus,
at block 610, the right atrium may be paced by an electrode located
within the right atrium, for example, atrial electrode 9, 13.
Alternatively, the left atrium may be paced by an electrode located
within the left atrium, for example, atrial electrode 9, 13.
Meanwhile, the right ventricle may be paced by an electrode located
within the right ventricle, for example, ventricular electrode 2,
3. Alternatively, the left ventricle may be paced by an electrode
located within the left ventricle, for example, ventricular
electrode 2, 3.
[0101] At block 715, it may be determined whether atrial
fibrillation is detected. This may be determined using any suitable
method known in the arts. For example, the sensing of a premature
atrial contraction (PAC) or a premature ventricular contraction
(PVC) is known in the art to indicate that atrial fibrillation is
occurring. The PAC/PVC may be sensed, for example, by one or more
of the sensing leads described above or by activity sensor 11. The
occurrence of atrial fibrillation may be determined, for example,
by an appropriate computer algorithm stored in memory or a portion
of memory of microcomputer 58 of IMD 10. This determination may
also be made as described above and illustrated in Graphs A-C. If
no atrial fibrillation is detected, the method returns to block 710
and the heart is paced at its regular pacing function.
Alternatively, the heart may be paced at any suitable value if no
atrial fibrillation occurs.
[0102] If atrial fibrillation is detected, the method may proceed
to block 720, when a first combipolar pacing therapy is delivered
to the ventricle. This may take the form of, for example, a single
combipolar pacing pulse. Combipolar pacing may be accomplished
using any suitable method known in the arts. In one embodiment,
leads 16 and 18 described above may be adapted to administer
combipolar pacing pulses to cardiac tissue. For example, lead 16
may be adapted to administer pacing pulses as an atrial lead and
lead 18 may be adapted to administer pacing pulses as a ventricular
lead, or vice versa. Thus, lead 16 and lead 18 may administer a
combipolar pulse by pacing at least one of the ventricles
simultaneously. In at least some embodiments of the invention, a
combipolar pulse may also be delivered in an alternating fashion,
for example, the ventricle may be paced with lead 16 and
immediately after with lead 18 or with lead 18 followed by lead 16.
In some embodiments of the invention, combipolar pacing is
preferably administered to the right ventricle. Alternatively a
combipolar pacing pulse may be administered to an area of the right
ventricle which bypasses right ventricle outflow tracks.
Alternatively, a combipolar pacing pulse may be administered to the
apex of the right ventricular sinus.
[0103] Alternatively, at least one of ventricular electrodes 2, 3
is used in a combipolar pacing fashion to induce a ventricular
extra-systole in conjunction with at least one of the atrial
electrodes 9, 13. Thus ventricular electrode 2,3 and atrial
electrode 9, 13 may administer a combipolar pulse by pacing at
least one of the ventricles simultaneously. In at least some
embodiments of the invention, a combipolar pulse may also be
delivered in an alternating fashion, for example, the ventricle may
be paced with ventricular electrode 2,3 and then with atrial
electrodes 9, 13 or vice versa, i.e., with atrial electrodes 9, 13
followed by ventricular electrodes 2, 3. In some embodiments of the
invention, combipolar pacing is preferably administered to the
right ventricle. Alternatively a combipolar pacing pulse may be
administered to an area of the right ventricle which bypasses right
ventricle outflow tracks. Alternatively, a combipolar pacing pulse
may be administered to the apex of the right ventricular sinus.
[0104] In another embodiment of the invention ring electrode 2 may
be adapted to administer pacing pulses as an atrial lead and coil
electrode 5 may be adapted to administer pacing pulses as a
ventricular lead, or vice versa. Thus, electrode 2 and electrode 5
may administer a combipolar pulse by pacing at least one of the
ventricles simultaneously. In at least some embodiments of the
invention, a combipolar pulse may also be delivered in an
alternating fashion, for example, the ventricle may be paced with
electrode 2 followed by electrode 5 or vice versa, i.e., the
ventricle may be paced with electrode 5 followed by electrode 2. In
some embodiments of the invention, combipolar pacing is preferably
administered to the right ventricle. Alternatively a combipolar
pacing pulse may be administered to an area of the right ventricle
which bypasses right ventricle outflow tracks. Alternatively, a
combipolar pacing pulse may be administered to the apex of the
right ventricular sinus.
[0105] In one embodiment of the invention, circuitry 63 may be used
to administer a combipolar pacing pulse by controlling pulses
delivered from one or more electrodes.
[0106] The combipolar pacing therapy preferably delivers an
effective amount of energy sufficient to terminate atrial
fibrillation. The combipolar pacing may create a field in the area
between the atrial and the ventricular leads. This field may cause
the paces delivered by one or more of the atrial and/or ventricular
leads to have a higher than normal amplitude or pulse width.
Alternatively, a low energy pulse may be delivered from the
combination of atrial and ventricular electrodes. In one embodiment
of the invention, each of the electrodes delivers the maximum
energy it is capable of delivering during administration of its
first combipolar pacing pulse. Alternatively, a combination of low
and high energy pulses may be administered as a first combipolar
pacing pulse. In one embodiment of the invention, the first
combipolar pacing pulse is administered for a duration long enough
to cause a ventricular extra-systole. In at least some embodiments
of the invention, a ventricular action is initiated after a 600 ms
duration. Other possible ranges of duration include, but are not
limited to 200 to 1000 ms, 300 to 900 ms, 400 to 800 ms, 500 to 700
ms and 550 to 650 ms.
[0107] At block 725, it may be determined if a ventricular
extra-systole has been induced. The ventricular extra-systole may
be sensed with any of the sensing electrodes described above. In
one embodiment of the invention, the ventricular extra-systole is
induced by the combipolar pacing of block 720. Detection of a
ventricular extra-systole may be accomplished using any suitable
method known in the arts. In one embodiment, one or more of sensing
leads 16 and 18 and/or activity sensor 11 described above may be
adapted to sense a ventricular extra-systole. Alternatively, at
least one of ventricular electrodes 2, 3 may sense the ventricular
extra-systole. In one embodiment of the invention, circuitry 63 may
be used to determine if a ventricular extra-systole has been
sensed.
[0108] In one embodiment of the invention, the ventricular
extra-systole will have a interval shorter than the ordinary
ventricular interval of the patient. This ordinary interval may be
determined and set by a physician, may be based on the patient's
medical history, may be a preprogrammed pacing interval, may be
selected from a look-up table or database, or calculated based on
data gathered by IMD 10.
[0109] In at least some embodiments of the invention, IMD 10 may
determine the given interval of the first two or more detected
atrial arrhythmia beats and will trigger delivery of the first
combipolar pacing therapy so that it is administered on at a point
in time which corresponds to the determined interval minus a
selectable percentage of the determined interval, i.e.,
3 time of combipolar = determined - percentage of pacing interval
interval determined interval
[0110] This percentage may be based on the vulnerable phase of the
T-wave. The T-wave phase may be sensed, for example using sensor 11
or the sensing electrodes described above. Alternatively, the
percentage may be calculated from a programmable dynamic refractory
period. This calculation may be accomplished, for example under the
control of any appropriate computer algorithm stored in a memory or
a portion of a memory of microcomputer 58 in IMD 10. Such a
computer algorithm may be any program capable of being stored in an
electronic medium such as, by way of example only, RAM 68 or ROM 70
of IMD 10, where the contents of RAM 68 and ROM 70 may be accessed
and consequently executed by microprocessor 64/microcomputer
58.
[0111] If a not induced ventricular action is detected with the
desired predetermined ordinary interval, a ventricular
extra-systole may have occurred and the method may proceed to the
optional step indicated at block 730. If a ventricular action is
detected with an interval shorter than the predetermined ordinary
interval concurrently succeeded by one or more ventricular actions
with intervals equal to or shorter than the predetermined ordinary
interval, a ventricular-couplet or run may have occurred and the
method may proceed to the optional step indicated at block 730.
Alternatively, the method may proceed to block 735.
[0112] The optional step indicated at block 730 may be used to help
curb any possible ventricular fibrillation that may result from the
administration of the combipolar pacing therapy. Thus, at block
730, a defibrillation pulse may be administered to the ventricle
following combipolar pacing. For example ventricular electrodes 2,
3 may be used to administer pacing pulses to the ventricle affected
by the combipolar pacing therapy. In a preferred alternative,
defibrillation electrode 5 is used to administer defibrillation
pulses to the ventricle affected by the combipolar pacing therapy.
Once the defibrillation pulse(s) have been administered, the method
may proceed to block 735.
[0113] At block 735, it may again be determined whether atrial
fibrillation is occurring. This may be determined using any
suitable method known in the arts. For example, the sensing of a
premature atrial contraction (PAC) or a premature ventricular
contraction (PVC) is known in the art to indicate that atrial
fibrillation is occurring. The PAC/PVC may be sensed, for example,
by one or more of the sensing leads described above or by activity
sensor 11. The occurrence of atrial fibrillation may be determined,
for example, by an appropriate computer algorithm stored in memory
or a portion of memory of microcomputer 58 of IMD 10. If atrial
fibrillation is no longer detected, the method returns to block 710
and the heart is paced at its regular pacing function.
Alternatively, the heart may be paced at any suitable value once
atrial fibrillation has been terminated. Before or while the heart
returns to ordinary pacing function, data regarding the number of
combipolar pacing therapies administered and the efficacy of the
therapies administered may be stored for later retrieval and
evaluation at block 750. This data may be stored, for example, in a
storage location of IMD 10, including but not limited to, a
location of memory 59 and/or RAM 68.
[0114] At block 735, determination if atrial fibrillation is still
occurring may be made using the methods described above and
illustrated in Graphs A-C, i.e., detecting an atrial arrhythmia
that may indicate the onset of atrial fibrillation, detecting an
atrial arrhythmia with an interval shorter than an predetermined
interval established for the patient, detecting a plurality of
atrial arrhythmias, and/or measuring the intervals of a plurality
of atrial arrhythmias. In another embodiment of the invention, IMD
10 may redetect the atrium and re-tune to the existing cycle
length. IMD 10 may then evaluate whether the existing cycle length
represents atrial arrhythmia.
[0115] If atrial fibrillation is still detected, the method may
proceed to block 740, when a next combipolar pacing therapy is
delivered to the ventricle. This make take the form of, for
example, a single combipolar pacing pulse. Combipolar pacing may be
accomplished using any suitable method known in the arts.
Combipolar pacing may be accomplished as described above using
leads 16 and 18, ventricular electrodes 2, 3 and atrial electrodes
9, 13, or using ring electrode 2 and coil electrode 5.
[0116] In one embodiment of the invention, circuitry 63 may be used
to administer a combipolar pacing pulse by controlling pulses
delivered from one or more electrodes.
[0117] The combipolar pacing therapy preferably delivers an
effective amount of energy sufficient to terminate atrial
fibrillation. The combipolar pacing may create a field in the area
between the atrial and the ventricular leads. This field may cause
the paces delivered by one or more of the atrial and/or ventricular
leads to have a higher than normal amplitude or pulse width.
Alternatively, a low energy pulse may be delivered from the
combination of atrial and ventricular electrodes. In one embodiment
of the invention, each of the electrodes delivers the maximum
energy it is capable of delivering during administration of its
first combipolar pacing pulse. Alternatively, a combination of low
and high energy pulses may be administered as a first combipolar
pacing pulse. In one embodiment of the invention, the first
combipolar pacing pulse is administered for a duration long enough
to cause a ventricular extra-systole. In at least some embodiments
of the invention, a ventricular action is initiated after a 600 ms
duration. Other possible ranges of duration include, but are not
limited to 200 to 1000 ms, 300 to 900 ms, 400 to 800 ms, 500 to 700
ms and 550 to 650 ms.
[0118] At block 745, the number of combipolar pacing therapies
delivered is calculated. Generally, only a limited number of
combipolar pacing therapies may be applied to cause ventricular
extra-systole. Moreover, administration of combipolar pacing
therapies may generally be successful in termination of atrial
fibrillation after the first, second or third delivery. Thus, at
block 745, it is determined if the number of combipolar pacing
therapies delivered exceeds a particular limit. For example, the
limit may be x number of combipolar pacing therapies. In one
embodiment of the invention, x may equal any suitable number for
ensuring optimal therapeutic benefit to the patient including, but
not limited to a maximum of 4 combipolar therapies, 3 combipolar
therapies and 2 combipolar therapies.
[0119] If the number of combipolar therapies delivered does not
exceed the limit set at block 745, the method may proceed to the
optional step indicated at block 730 or to block 735 as indicated
by the loop at 747. The optional step indicated at 730 may be used
to help curb any possible ventricular fibrillation that may result
from the administration of the combipolar pacing therapy. Thus, at
block 730, a defibrillation pulse or pulses may be administered to
the ventricle following combipolar pacing.
[0120] Alternatively, at block 735, it may again be determined
whether atrial fibrillation is occurring. This may be determined
using any suitable method known in the arts or described above. If
atrial fibrillation is no longer detected, the method returns to
block 710 and the heart is paced at its regular pacing function.
Alternatively, the heart may be paced at any suitable value once
atrial fibrillation has been terminated. Before or while the heart
returns to ordinary pacing function, data regarding the number of
combipolar pacing therapies administered and the efficacy of the
therapies administered may be stored for later retrieval and
evaluation at block 750. This data may be stored, for example, in a
storage location of IMD 10, including but not limited to, a
location of memory 59 and/or RAM 68.
[0121] In some embodiments of the invention, an optional step as
indicated at block 737 may include administering a defibrillation
pulse or pulses before the method returns to block 710. The
optional step indicated at 737 may be used to help curb any
possible ventricular fibrillation that may result from the
administration of the combipolar pacing therapy. Thus, at block
737, a defibrillation pulse may be administered to the ventricle
following combipolar pacing.
[0122] If atrial fibrillation is still detected, the method may
proceed to block 740, when a next combipolar pacing therapy is
delivered to the ventricle. The loop indicated at 747 may be
repeated until administration of combipolar pacing therapy
effectively terminates atrial fibrillation or until the limit of
combipolar pacing therapies indicated at block 745 is exceeded.
[0123] At block 745, when the limit of combipolar pacing therapies
has been exceeded, the method may return to block 710 and the heart
is paced at its regular pacing function. Alternatively, the heart
may be paced at any suitable value once atrial fibrillation has
been terminated. Before or while the heart returns to ordinary
pacing function, data regarding the number of combipolar pacing
therapies administered and the efficacy of the therapies
administered may be stored for later retrieval and evaluation at
block 650. This data may be stored, for example, in a storage
location of IMD 10, including but not limited to, a location of
memory 59 and/or RAM 68.
[0124] In some embodiments of the invention, an optional step as
indicated at block 737 follows block 746. This optional step may
include administering a defibrillation pulse or pulses before the
method returns to block 710. The optional step indicated at 737 may
be used to help curb any possible ventricular fibrillation that may
result from the administration of the combipolar pacing therapy.
Thus, at block 737, a defibrillation pulse may be administered to
the ventricle following combipolar pacing.
[0125] In the embodiments of the invention seen in FIGS. 6 and 7,
the parameters determined include: initial pacing function value,
combipolar pacing function value, detection of ventricular
extra-systole, and duration of combipolar pacing. One or any
suitable combination of these parameters may be varied in
accordance with the present invention. Alternatively, one or more
of these parameters may be set at a desired value while one or more
other parameters are varied in accordance with the present
invention. Moreover, although the parameters are shown as being
determined in a given order, these parameters may be determined in
any combination and in any order in accordance with the present
invention.
[0126] The preceding specific embodiments are illustrative of the
practice of the invention. It is to be understood, therefore, that
other expedients known to those skilled in the art or disclosed
herein, may be employed without departing from the invention or the
scope of the appended claims. For example, the present invention is
not limited to a method for increasing a pacing parameter of a
mammalian heart. The present invention is also not limited to the
termination of atrial fibrillation or the induction of ventricular
extra-systole, per se, but may find further application as a means
of administering pacing therapy. The present invention further
includes within its scope methods of making and using the
measurement means described hereinabove.
[0127] In the claims, means-plus-function clauses are intended to
cover the structures described herein as performing the recited
function and not only structural equivalents, but also equivalent
structures. Thus, although a nail and a screw may not be structural
equivalents in that a nail employs a cylindrical surface to secure
wooden parts together, whereas a screw employs a helical surface,
in the environment of fastening wooden parts a nail and a screw are
equivalent structures.
* * * * *